(AP)

Serena Williams won her 19th Grand Slam on Saturday night in Melbourne, breaking a tie with Chris Evert and Martina Navratilova and putting her within three of tying Steffi Graf’s Open era record of 22. With Serena so close, the question now becomes: Can Serena surpass Steffi?

Predicting the unknowable is impossible, but it’s made harder in this case because there’s no comparison for Serena Williams. No other tennis player in history dominated the sport into his or her 30s, let alone at age 33. Heck, Graf had already been retired for three years by the time she was Serena’s current age.

(AP)

But it’s not as if Serena is winning these Slams with a walker and sipping a cup of chamomile. She’s in complete command of her sport. She’s not sneaking in Slams like Martina was at the end of her career, she’s looking unbeatable in most.

No one beats Serena Williams unless she beats herself. That’s what happened at the first three Slams last year, when Serena lost precious time in her bid to pass Graf because she lost control of matches she should have won. But two easy wins at the U.S. Open and Australian Open puts her back on track. (How good was Serena in Melbourne? She faced nine break points from the quarterfinals on.)

(Getty Images)

But for as good as she is, can Serena keep it up at 34 and 35, the ages she’ll have to be to pass Graf? (And passing is the only goal here. On ESPN, the studio analysts were talking about the three Slams Serena needs to tie Graf, but that’s no good. Tying is like kissing you sister. Though I’m sure Serena will happily give a peck on the cheek to Venus, it wouldn’t be for this. Four is the number. No. 23 is the goal.)

Serena defeated Steffi at Indian Wells in 1999. (AP)

Even with a “disappointing” 2014, Serena has won six of the past 11 Grand Slams. At that rate, she’d pass Graf at next year’s U.S. Open. How did we come up with that number? Serena won four of her last eight Slams. Before that she won four of six. This prediction splits the difference and assumes four of the next seven.

But what if we follow her declining Grand Slam win percentage and assume four of the next 10 instead. That would give her the record at Wimbledon in 2017, when she’ll be 35 years old.

Can we keep assuming dominance, however? In winning on Saturday, Serena became the second-oldest female winner of a Grand Slam in history. Navratilova was four months older won she won her final of her record nine Wimbledons in 1990. Given that the French Open isn’t for four months, Serena will have to set the record for oldest female Slam winner a total of four times in order to pass Graf.

Navratilova was on hand Saturday to watch Serena surpass her. (Getty Images)

That won’t be a problem who’s as mentally focused as Serena is now. In the middle of her career, she seemed to lose the desire to play. From 2005-2008 she won 1 of 14 Slams due to injuries and apathy. I doubt she gets complacent now. With a coach she credits for motivating her in Patrick Mouratoglou and the possibility of solidifying her place as the all-time great in women’s tennis, it’s hard to imagine Serena slowing down.

But things can happen. Injuries, outside interests taking over, a desire to become a mother (which Serena has spoken about before): anything can knock her off the rails. Remember back in 2008 when Tiger Woods was sure to be challenging Jack Nicklaus’ record right about now? That’s not to say Serena is going to have any Tiger-like incidents, but life is unpredictable. Something that looks so attainable today can be so far to grasp down the road.

No. 1. Serena celebrates her win at the 1999 U.S. Open. (AP)

Still, I think she does it. Serena is set on playing until at least the 2016 Olympics (she and Venus are playing on the Fed Cup in order to qualify), which is six Grand Slams from now. Win just two of those and she’s one behind Graf. If she’s not already motivated now, getting to No. 21 and being so close will have her desperate to get to No. 22 and beyond.

Of course, there’s the little matter of getting to No. 20 and Serena isn’t taking it for granted.

(Getty Images)

“I would love to get to 22,” Serena told reporters in Melbourne, “but I have to get to 20 first.” (Prediction: She gets to No. 20 by the end of the summer.)

Even if she retired today, Serena Williams will likely go down as the greatest player in women’s tennis history. But over the next few years, expect her to continue defying the odds. She’ll break Graf’s Grand Slam record to end all discussion on the matter of who’s the greatest ever. Though the record-breaker could come as early as next year’s Australian Open, I’ll peg No. 23 as coming at the U.S. Open in 2017.

Never doubt, or count out, Serena Williams.

(AP)